Q: aaplatt

Delta update, which will only update 10.6.7 to 10.6.8.

Combo update, which will update any version from 10.6.0 - 10.6.7 up to 10.6.8.

There isn't an update. Apple stopped doing them for 10.6 a couple of years ago. There is an upgrade to 10.7, if your computer can be upgraded.

Software update, upgrade--what's the difference? - http://support.apple.com/kb/HT1444

OS X: Updating OS X and Mac App Store apps - http://support.apple.com/kb/HT1338

Reference releases; update vs. upgrade

Check this site to see what is possible:

Everymac web site with Apple model listing - http://www.everymac.com/systems/apple/index-apple-specs-applespec.html

Then look into buying the necessary upgrade using the Mac App Store app.